THE BRAIN: HEARING AND LANGUAGE

THE BRAIN: HEARING AND LANGUAGE

The brain processes hearing and language in distinct but highly interconnected areas, primarily located within the temporal lobe and the surrounding cortices, usually in the left hemisphere (for language).

👂 Hearing (Auditory Processing)

The initial conscious perception and analysis of sound occur in the Primary Auditory Cortex (A1).

• Location: Located in the Temporal Lobe on the superior temporal gyrus, often hidden deep within the lateral sulcus (Sylvian fissure) on a structure called Heschl's gyrus.

• Function: It is the first cortical area to receive auditory information relayed from the inner ear (cochlea) and thalamus.

  • It analyzes basic sound properties like pitch (frequency), loudness (intensity), and timing.

  • It contains a tonotopic map, meaning different areas respond best to different sound frequencies, mirroring the organization of the cochlea.

• Pathway: After initial processing in A1, the sound information is sent to surrounding secondary and association cortices for more complex interpretation, such as recognizing whether the sound is speech, music, or an environmental noise.

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🗣️ Language (Comprehension and Production)

In most right-handed individuals (and a majority of left-handed people), the critical language centers are lateralized to the left cerebral hemisphere. The two most famous areas form a functional loop:

1. Wernicke's Area (Comprehension)

• Location: Located in the posterior part of the Superior Temporal Gyrus of the temporal lobe, often extending into the adjacent parietal lobe.

• Function: This area is responsible for language comprehension. It processes incoming speech (after initial acoustic analysis in the auditory cortex) and written words, allowing you to understand the meaning of language.

• Damage: Lesions lead to Wernicke's Aphasia (or receptive aphasia), where a person can speak fluently and with correct grammar, but the speech often lacks meaning ("word salad"), and they have severe difficulty understanding spoken or written language.

2. Broca's Area (Production)

• Location: Located in the posterior part of the Inferior Frontal Gyrus of the frontal lobe.

• Function: This area is crucial for language production. It helps formulate thoughts into coherent grammatical sentences and manages the planning and programming of the motor movements required for speech (articulation).

• Damage: Lesions lead to Broca's Aphasia (or expressive/motor aphasia), where a person understands language but struggles to produce fluent speech. Their speech is often slow, non-fluent, and agrammatical.

Connection

These two areas are connected by a bundle of nerve fibers called the Arcuate Fasciculus, which allows communication between comprehension and production centers, important for repeating words and phrases.

In the general population, 95 percent of people are right-handed, which means that the left hemisphere is the dominant hemisphere. (For you left-handers, the right hemisphere is dominant.) With right-handed people, the ability to understand and express language is in this left temporal lobe. If I were to take a metal probe, and charge it with just a bit of electricity, and put it on the "primary" area of my left temporal lobe, I might say "hey, I hear a tone." If I move this probe to a more complex area of the temporal lobe, I might hear a word being said. If I move the electrical probe to an even more complex area, I might hear the voice of somebody I recognize; "I hear Uncle Bob's voice." We have simple areas of the temporal lobe that deal with basic sounds and other areas of the temporal lobe that look at more complex hearing information.

The right temporal lobe also deals with hearing. However, its job is to process musical information or help in the identification of noises. If this area is damaged, we might not be able to appreciate music or be able to sing. Because we tend to think and express in terms of language, the left temporal lobe is more critical for day-to-day functioning.

The vision areas and the hearing areas of the brain have a boundary area where they interact. This is the area of the brain that does reading. We take the visual images and convert them into sounds. So if you injure this area (or it doesn't develop when you are very young), you get something called dyslexia. People who have dyslexia have problems that may include seeing letters backwards or have problems understanding what written words mean.

THE BRAIN: HEARING AND LANGUAGE: VIDEO

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Diagram of brain: human movement.